1. Field of the Invention
This invention relates to photographic objectives of small size having a reduced number of constituent lenses with the total length of the lens system being shortened to suit for wide angle shooting.
2. Description of the Prior Art
Recently, as the trend of cameras in minimization of their bulk and size advances, there are increasing demands for small-sized photographic objectives with a shortening of the total length of the lens system. Particularly in respect to the ratio of the total length L of the lens system measured from the front vertex to the focal plane to the focal length f, or the so-called telephoto ratio L/f, it is desired that its value is taken at less than unity. For this purpose, it is preferred to construct the lens system from a front lens group of positive power and a rear lens group of negative power. Such power distribution has found its many used in photographic objectives for long focal length with narrow angular field coverage which are of the so-called telephoto type, but there are a few examples of acceptance in objectives of wider angular field coverage than the standard one. This is because the shortening of the total length of the lens system under the condition of this power distribution causes distortion, field curvature, astigmatic difference and coma to increase as the image angle increases. As such objective, though being few in number, mention can be made of several ones. For example, in Japanese Patent No. Sho 44-10831, an objective having an image angle on the order of those of the standard ones is described. Also U.S. Pat. No. 3,998,527 discloses an objective of which the total length is shortened though it is somewhat slow as the F-number is 4.5, while U.S. Pat. Nos. 4,235,521 and 4,303,313 providing objectives of increased image angle while still preserving fast F-numbers, though the total length is somewhat elongated as the telephoto ratio is nearly unity.